Rocket fuel



Jnited States Patent ration No Drawing. Filed Nov. 2, 1959, Ser. No. 850,067 5 Claims. (Cl. 60-35.4)

This invention relates to improved rocket fuels. More articularly, this invention relates to rocket fuels comrising nitric acid and an organic compound which is :ficient in oxygen, e.g. chloronitrobenzene, pyridine, or le like.

A satisfactory rocket fuel must contain both a comustible substance and an oxygen supplier for the comustion of that substance. Generally such rocket fuels :quire great care in handling because of their tendency spontaneously ignite at room temperatures. Typical f the prior art rocket fuels are solutions of nitric acid nd aromatic polynitro compounds, for example, a soluon of nitric acid and meta-dinitrobenzene. The polyitro compound, in this case the meta-dinitrobenzene, is he actual fuel, the ntiric acid serving to supply oxygen ontinuously thereto so as to ensure complete combustion f the dinitrobenzene.

As is well known, the nitration of aromatic compounds an exothermic reaction resulting in the liberation of a onsiderable amount of heat. Accordingly, when using a nitric acid solution of m-dinitrobenzene as a rocket fuel he exothermic heat of nitration is not available as energy :ontent in the rocket fuel, so that the heat of combustion if the fuel is considerably less than it would have been lad such exothermic energy of nitration been available. [his results in a less efficient and less powreful rocket fuel.

Accordingly, it is an object of this invention to provide mproved rocket fuels capable of burning with higher leats of combustion than previously thought possible.

Another objects to provide rocket fuels that are stable it ordinary temperatures and not prone to self ignition whereby they may be readily handled with comparative iafety yet without requiring undue precautions.

Additional objects will become apparent hereinafter.

In accordance with one aspect of this invention, rocket Euels of unusually high energy contnt are provided by mixing nitric acid with an organic compound that is both clefinient in oxygen and also resistant to nitric acid. Such a compound should be resistant to nitric acid even when the acid is heated to its boiling point. These organic compounds are preferably aromatic or heterocyclic.

Suitable oxyen-deficient aromatic compounds that resist reaction with nitric acid include the halonitrobenzenes, e.g. chloronitrobenzene, and pyridine. If chloronitrobenzene is used, any of the ortho-, meta-, or para isomers is satisfactory, either alone or as mixed with one or both of the other two isomers.

The mixture of the nitric acid with a suitable oxygendeficient aromatic compound should preferably contain about 60-80% by weight of concentrated nitric acid and correspondingly about -40% by weight of the oxygendeficient compound.

In accordance with a preferred aspect of my invention, one or more metals or metal hydrides are added to the nitric acid-oxygen-deficient compound solution. Suitable metals include aluminum, boron, and lithium. The corresponding hydrides of these metals are equally applicable. The addition of such metals to the nitric acid-oxygen-deficient compound mixture serves a dual purpose in that (1) the combustion temperature of the fuel is further increased, thereby resulting in greater power and efliciency and (2) the specific weight of thefuel is increased. The amount of metal or metal hydride added is preferably from 1 to 40 percent (by weight) of the weight of the nitric acid-oxygen-deficient compound solution.

The nitric acid-halonitrobenzene rocket fuels of this invention are readily prepared by simply reacting nitric acid with a suitable monohalogenated benzene. The resulting halonitrobenzene compound is resistant to further nitration from excess nitric acid, even when such aCld is at its boiling point. Typical of the monohalobenzenes to be reacted with nitric acid is monochlorobenzene. Upon nitration of chlorobenzene with nitric acid there results mononitrochlorobenzene. This is resistant to further attack by the nitric acid.

It will be noted that by a single nitration of chlorobenzene with excess nitric acid there is at once obtained a mixture which is an improved rocket fuela fuel of high energy content and proper oxygen balance which, upon ignitlon, burns with an unusually high heat of combustron. That is, this mixture comprises chloronitrobenzene (the combustible of the rocket fuel) and excess nitric acid. Upon ignition of the chloronitrobenzene combustible the nitric acid functions both as an oxygen supplier and also as a nitrating agent therefor, thereby introducing additional nitro groups into the combustible with the consequent liberation of considerable heat (since this nitration reaction is highly exothermic). Accordingly, the combustion temperature is greatly elevated.

The following examples will more fully illustrate this invention. All parts are by weight unless otherwise indicated.

Example 1 Twenty-five parts of chlorobenzene were added with cooling and agitatin to parts of concentrated (98%) nitric acid. The heat of the reaction indicated a mononitration of the chlorobenzene had occurred. There resulted a mixture of three (ortho, meta, and para) chloronitrobenzene isomers along with excess nitric acid. No dinitration occurred. The chloronitrobenzene isomers were each resistant to further nitration, by the nitric acid so that the heat capable of being liberated by any further exothermic nitrations was maintained as potential energy of the rocket fuel. Upon proper ignition of this mixture in a rocket the heat of combustion, as determined by the thrust developed, was considerably greater than that developed by a similar fuel wherein m-dinitrobenzene was substituted for the chloronitrobenzene.

Example 2 To parts of concentrated (98%) nitric acid were added, with cooling, 20 parts of pyridine. The amount of heat liberated was precisely the calculated theoretical amount that would be expected to be developed upon the neutralization of a base (pyridine) by an acid. No nitration of the pyridine occurred. The heat capable of being liberated by any subsequent exothermic nitration of the pyridine was maintained as potential energy of the rocket fuel. Upon proper ignition of the above mixture there was developed a very large heat of combustion-much greater than that developed by a similar fuel wherein m-dinitrobenzene was substituted for pyridine.

It will be noted that when a monohalobenzene is treated with nitric acid (Example 1) there is a mononitration resulting in a halonitrobenzene. This halonitrobenzene resists further attack by the nitric acid. However, when pyridine is treated with nitric acid (Example 2) not even mononitration occurs, for the pyridine merely dissolves in the acid. Of course, subsequent ignition of the product of Example 2 does cause exothermic nitration of the pyridine.

Example 3 To the mixture of nitric acid and chloronitrobenzene produced in Example 1 were added with stirring 25 parts of powdered aluminum metal. There resulted a mixture that was eminently suitable as a rocket fuel in that it had a high combustion temperature, a high specific weight, and was capable of liberating a considerable heat of combustion.

Example 4 To the solution of pyridine in nitric acid produced by Example 2 were added with stirring 35 parts of powdered lithium hydride. The resulting mixture was also an excellent rocket fuel by virtue of its high specific weight, high combustion temperature, and high heat of combustion.

It will of course be understood that the foregoing detailed description and examples are given merely by way of illustration, and that many variations can be made therein without departing from the spirit of the invention. For example, another halogenated benzene, e.g. bromobenzene, might be substituted for the chlorobenzene of Example 1, leading to a mixture of nitric acid and brornonitrobenzene, which mixture would also exemplify an improved rocket fuel of this invention. Similarly another metal or metal hydride, e.g. powdered boron or boron hydride, could be substituted for the aluminum of Example 3 or the lithium hydride of Example 4.

Having thus described my invention, what I desire to claim and secure by Letters Patent is:

1. A method of producing thrust which comprises ejecting from a reaction chamber the gaseous products produced by the combustion of a fuel comprising a mixture of concentrated nitric acid and a halomononitrobenzen-e.

2, The method of claim 1 wherein said mixture contains from 60 to 80 weight percent of nitric acid and from 20 to 40 weight percent of said halomononitrobenzene.

3. The method of claim 1 wherein said fuel contains from 1 to 40 weight percent, based on the amount of 5 said mixture, of a material selected from the group consisting of aluminum, boron, lithium, and their hydrides.

4. A rocket fuel consisting essentially of (1) a mixture of from 60 to 80 weight percent concentrated nitric acid and from 20 to 40 weight percent pyridine and (2) from 1 to 40 Weight percent, based on the total amount of said mixture, of a material selected from the group consisting of aluminum, boron, lithium, and their hydrides.

5. A rocket fuel comprising a mixture containing from about 60 to 80 parts by weight of concentrated nitric acid and correspondingly from about to 40 parts by weight of halomononitrobenzene, and containing from 1 to 40 parts by weight of a material selected from the group consisting of almuminum, boron, lithium, and their hy- 20 drides.

References Cited in the file of this patent UNITED STATES PATENTS 2,749,372 Dittmar June 5, 1956 2,774,214 Malina et al Dec. 18, 1956 2,810,000 Schenck 0a. 15, 1957 OTHER REFERENCES Journal of Chemical Education, Penner, January 1952, pages 37-39.

Ind. and Eng. Chem, vol. 48, No. 4, April 1956, pages 722-724.

C and En, June 23, 1958, pages 62 67. Spindler: Ann. Chem., vol. 224 (1884), pp. 283-313 (only pp. 299 to 301 relied on). 

1. A METHOD OF PRODUCING THRUS WHICH COMPRISES EJECTING FROM A REACTION CHAMBER THE GASEOUS PRODUCTS PRODUCED BY THE COMBUSTION OF A FUEL COMPRISING A MIXTURE OF CONCENTRATED NITRIC ACID AND A HALOMONONITROBENZE.
 5. A ROCKET FUEL COMPRISING A MIXTURE CONTAINING FROM ABOUT 60 TO 80 PARTS BY WEIGHT OF CONCENTRATED NITRIC ACID AND CORRESPONDINGLY FROM ABOUT 20 TO 40 PARTS BY WEIGHT OF HALOMONONITROBENZENE, AND CONTAINING FROM 1 TO 40 PARTS BY WEIGHT OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALMUMINUM, BORON, TITHIUM, AND THEIR HYDRIDES. 